Method and apparatus for transmitting and receiving time division duplex frame configuration information in wireless communication system

ABSTRACT

A method and an apparatus for transmitting and receiving Time Division Duplex (TDD) frame configuration information are disclosed. The base station transmits TDD frame configuration information as system information to a user equipment through a common control channel so as to dynamically change the TDD frame configuration according to uplink and downlink traffic conditions. The base station may deliver the same system information to all user equipments in the cell, removing ambiguity in User Equipment (UE) operations and avoiding interference. In comparison to an existing method of delivering TDD frame configuration information through system information update, the disclosed method enables user equipments to rapidly cope with traffic changes. In addition, user equipments may receive and apply TDD frame configuration information at the same time.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of Koreanpatent applications filed on Jun. 20, 2011 and May 9, 2012 in the KoreanIntellectual Property Office and assigned Serial Nos. 10-2011-0059727and 10-2012-0049056, respectively, the entire disclosure of each ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system. Moreparticularly, the present invention relates to a method and an apparatusfor transmitting and receiving configuration information on TimeDivision Duplex (TDD) frames having a dynamic subframe.

2. Description of the Related Art

Orthogonal Frequency Division Multiplexing (OFDM) transmission is amulti-carrier transmission scheme using multiple carriers for datatransmission. In OFDM, a serial input symbol stream is divided intomultiple parallel streams, which are then mapped to multiple orthogonalsub-carriers. Each sub-carrier is modulated by the corresponding streamwith a specified modulation scheme for transmission.

Multi-carrier modulation was first applied to high frequency militaryradio in the late 1950s. Although OFDM modulation techniques usingmultiple orthogonal sub-carriers have been developed since the 1970s,practical applications thereof have been limited owing to difficulty ofimplementing orthogonal modulation between multiple sub-carriers. Asignificant breakthrough in OFDM applicability was made in 1971(Weinstein et al.) by applying Discrete Fourier Transform (DFT) andInverse DFT (IDFT) to OFDM techniques. Use of DFT and IDFT has made OFDMmodulation and demodulation feasible. In addition, use of guardintervals and insertion of Cyclic Prefix (CP) symbols in guard intervalshave significantly reduced negative impacts of multipath reception anddelay spread on the system.

Thanks to such technical advances, OFDM techniques have been applied tovarious digital transmission schemes, such as Digital Audio Broadcasting(DAB), Digital Video Broadcasting (DVB), Wireless Local Area Networking(WLAN) and Wireless Asynchronous Transfer Mode (WATM). That is, use ofOFDM techniques had been limited owing to high hardware complexity inthe past, but recent advances in various digital signal processingtechniques including Fast Fourier Transform (FFT) and Inverse FastFourier Transform (IFFT) have made OFDM implementation practical.

Although similar to existing Frequency Division Multiplexing (FDM), OFDMis highly efficient in high speed transmission by maintainingorthogonality between multiple tones. As OFDM exhibits high frequencyefficiency and is robust against multi-path fading, it can achieveoptimum transmission efficiency in high speed data transmission.

Further, OFDM exhibits high frequency efficiency as it uses frequencyspectra in an overlapping manner, is robust against frequency selectivefading and multi-path fading, can reduce Inter-Symbol Interference (ISI)using a guard interval, can be implemented with an equalizer having asimple hardware structure, and is robust against impulse noise. Withthese advantages, OFDM is actively utilized for structuringcommunication systems.

In wireless communication, adverse channel conditions may hinder highquality data services. Channel conditions in wireless communication mayfrequently change owing to Additive White Gaussian Noise (AWGN), changesin received signal power due to fading, shadowing, Doppler effects dueto movement and speed changes of a user equipment, and interferencecaused by other users and multi-path signals. Hence, effectively copingwith such adverse channel conditions may be needed to support high speedand high quality data services in wireless communication.

In OFDM, modulation signals are on a two dimensional time-frequencyresource grid. Resources in the time domain are distinguished bydifferent orthogonal OFDM symbols. Resources in the frequency domain aredistinguished by different orthogonal tones. That is, in thetime-frequency resource grid, one OFDM symbol on the time axis and onetone on the frequency axis can specify a minimum resource unit that isreferred to as a Resource Element (RE). As different resource elementsare orthogonal to each other even after passing through frequencyselective channels, signals sent through different resource elements canbe received at the receiver side without causing interferencetherebetween.

A physical channel is a channel on the physical layer that is used totransmit modulation symbols obtained by modulating one or more coded bitstreams. In an Orthogonal Frequency Division Multiple Access (OFDMA)system, multiple physical channels are created according to usage ofinformation streams to be transmitted or types of receivers. Thetransmitter and receiver have to make a prior agreement on how toarrange a physical channel on what resource elements (mapping rule).

A wireless communication system may operate in a Frequency DivisionDuplex (FDD) mode or a TDD mode. In the FDD mode, two differentfrequencies are used for uplink and downlink transmission, and the basestation and user equipment may send and receive data at the same time.In the TDD mode, the same frequency is used for uplink and downlinktransmission, and the base station and user equipment cannot send andreceive data at the same time. Hence, in the TDD mode, the base stationand user equipment have to make a prior agreement on the time fortransmission.

Therefore, a need exists for a method and an apparatus for transmittingand receiving TDD frame configuration information in a wirelesscommunication system, wherein the base station sends TDD frameconfiguration information through a pre-specified region of the commoncontrol channel to thereby dynamically change the TDD frameconfiguration.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a method and an apparatus for transmitting andreceiving Time Division Duplex (TDD) frame configuration information ina wireless communication system, wherein the base station sends TDDframe configuration information through a pre-specified region of thecommon control channel to thereby dynamically change the TDD frameconfiguration, so that the base station may adaptively cope with uplinkand downlink traffic conditions and interference caused by simultaneoustransmission of the base station and user equipment owing to an error incontrol channel reception of the user equipment may be prevented.

In accordance with an aspect of the present invention, a method oftransmitting TDD frame configuration information for a base station in awireless communication system is provided. The method includesdetermining a TDD frame configuration by assigning a transmissiondirection to a dynamic subframe in a TDD frame, generating systeminformation based on information on the TDD frame configuration, andtransmitting the system information by inserting the system informationinto a common control channel.

The generating of the system information may include making the size ofthe system information equal to that of Downlink Control Information(DCI) for the common control channel. The generating of the systeminformation may also include attaching a Cyclic Redundancy Check (CRC)sequence scrambled with a Radio Network Temporary Identifier (RNTI)defined for TDD frame configuration information to the systeminformation. The generating of the system information may furtherinclude aggregating individual TDD frame configuration information ofmultiple carriers used in the wireless communication system into thesystem information.

In accordance with another aspect of the present invention, a method ofreceiving TDD frame configuration information for a user equipment in awireless communication system is provided. The method includes receivingsystem information on a common control channel, identifying a TDD frameconfiguration indicating a transmission direction of a dynamic subframein a TDD frame by analyzing the system information, and utilizing thedynamic subframe according to the transmission direction thereof.

The system information may have a size equal to that of DCI for thecommon control channel. Receiving system information may includeconducting blind decoding of the common control channel with an RNTIdefined for TDD frame configuration information. The system informationmay be system information created by aggregating individual TDD frameconfiguration information of multiple carriers used in the wirelesscommunication system.

In accordance with another aspect of the present invention, an apparatusfor transmitting TDD frame configuration information in a base stationof a wireless communication system is provided. The apparatus includes acontroller for determining a TDD frame configuration by assigning atransmission direction to a dynamic subframe in a TDD frame, a systeminformation generator for generating system information based oninformation on the TDD frame configuration, and a control channelgenerator for inserting the system information into a common controlchannel for transmission.

The system information generator may make the size of the systeminformation equal to that of DCI for the common control channel. Thesystem information generator may attach a CRC sequence scrambled with anRNTI defined for TDD frame configuration information to the systeminformation. The system information generator may aggregate individualTDD frame configuration information of multiple carriers used in thewireless communication system into the system information.

In accordance with another aspect of the present invention, an apparatusfor receiving TDD frame configuration information in a user equipment ofa wireless communication system is provided. The apparatus includes acontrol channel receiver for receiving system information on a commoncontrol channel, a system information analyzer for identifying a TDDframe configuration indicating a transmission direction of a dynamicsubframe in a TDD frame by analyzing the system information, and acontroller for utilizing the dynamic subframe according to thetransmission direction thereof.

The system information may have a size equal to that of DCI for thecommon control channel. The control channel receiver may include a blinddecoder that conducts blind decoding of the common control channel withan RNTI defined for TDD frame configuration information. When multiplecarriers are used in the wireless communication system, the systeminformation may be created by aggregating individual TDD frameconfiguration information of the multiple carriers.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an overview of a wireless communication systemaccording to an exemplary embodiment of the present invention;

FIG. 2 illustrates a Time Division Duplex (TDD) frame structureaccording to an exemplary embodiment of the present invention;

FIG. 3 illustrates a format of generic control channel informationaccording to an exemplary embodiment of the present invention;

FIG. 4 illustrates a format of control channel information according toan exemplary embodiment of the present invention;

FIG. 5 depicts transmission of TDD frame configuration informationaccording to an exemplary embodiment of the present invention;

FIG. 6 illustrates timing relationships between reception andapplication of TDD frame configuration information according to anexemplary embodiment of the present invention;

FIG. 7 illustrates a control channel format for TDD frame configurationinformation according to an exemplary embodiment of the presentinvention;

FIG. 8 illustrates a format of a MAC message used to carry TDD frameconfiguration information according to an exemplary embodiment of thepresent invention;

FIG. 9 is a flowchart of a transmission procedure for a base stationaccording to an exemplary embodiment of the present invention;

FIG. 10 is a flowchart of a reception procedure for a user equipmentaccording to an exemplary embodiment of the present invention;

FIG. 11 is a block diagram of a base station according to an exemplaryembodiment of the present invention; and

FIG. 12 is a block diagram of a user equipment according to an exemplaryembodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

FIGS. 1 through 12, discussed below, and the various exemplaryembodiments used to describe the principles of the present disclosure inthis patent document are by way of illustration only and should not beconstrued in any way that would limit the scope of the disclosure. Thoseskilled in the art will understand that the principles of the presentdisclosure may be implemented in any suitably arranged communicationssystem. The terms used to describe various embodiments are exemplary. Itshould be understood that these are provided to merely aid theunderstanding of the description, and that their use and definitions inno way limit the scope of the invention. Terms first, second, and thelike are used to differentiate between objects having the sameterminology and are in no way intended to represent a chronologicalorder, unless where explicitly stated otherwise. A set is defined as anon-empty set including at least one element.

The following description is focused on Long Term Evolution (LTE) andLTE-Advanced (LTE-A) systems operating in a Time Division Duplex (TDD)mode. However, exemplary embodiments of the present invention are alsoapplicable to other wireless communication systems supporting basestation scheduling and TDD mode operation without significantmodification.

In the LTE system, Orthogonal Frequency Division Multiplexing (OFDM) isapplied to downlink and Single Carrier-Frequency Division MultipleAccess (SC-FDMA) is applied to uplink. The LTE system may operate in aFrequency Division Duplex (FDD) mode or a TDD mode. During the FDD mode,two frequency bands are used respectively for uplink transmission anddownlink transmission. During the TDD mode, one frequency band is usedalternately for uplink transmission in one time period and downlinktransmission in another time period according to a preset rule. In LTETDD mode, radio frames may have seven uplink/downlink configurations.Once the TDD frame configuration is determined in the system, it israrely changed. To avoid severe interference between uplink transmissionand downlink transmission among cells, neighboring cells should have thesame TDD frame configuration for synchronization.

In TDD and FDD modes, one subframe is 1 ms long in time and LTEtransmission bandwidth wide in frequency, and includes two slots intime. In the frequency domain, subcarriers (i.e., tones) are groupedinto Resource Blocks (RBs), which are used as a basic unit for resourceallocation. One resource block may include 12 tones in frequency and 14OFDM symbols in time (slot). Each subframe includes a control channelregion for control channel transmission and a data channel region fordata channel transmission, and Reference Signals (RSs) for channelestimation are inserted into the control and data channel regions.

Recently, research and development has been conducted on the LTE-Asystem as an evolved version of the LTE system. In TDD mode of the LTE-Asystem, similarly to the case of the LTE system, once the TDD frameconfiguration is determined, it cannot be readily changed, resulting inthe inability to dynamically cope with changes in data traffic. That is,although uplink data traffic significantly increases for a certain time,unused downlink subframes are not usable for transmitting increaseduplink traffic. Such a problem tends to occur in the presence of ahierarchy of cells. This is further described with reference to FIG. 1.

FIG. 1 illustrates an overview of a wireless communication systemaccording to an exemplary embodiment of the present invention. In thewireless communication system, macro cells and picocells arehierarchically arranged in the same area.

Referring to FIG. 1, reference numerals 101 and 102 indicate a macrocell and a picocell, respectively. A picocell is typically installed atan area where data traffic demand is high within the coverage area of amacro cell. In the picocell, lower transmit power is used than in themacro cell. Even in the same area, data traffic demand may dynamicallychange with time. For example, when many users request data receptionand Voice over IP (VoIP) reception and transmission, downlink trafficdemand is high and uplink traffic demand is low. The system then selectsa TDD frame configuration that allocates a large number of subframes todownlink and allocates a small number of subframes to uplink. At a latertime, when many users request data transmission and VoIP transmission,there is a rapid increase in uplink resource demand. It is difficult tohandle such a situation with normal system configurations.

FIG. 2 illustrates a TDD frame structure according to an exemplaryembodiment of the present invention.

Referring to FIG. 2, in an LTE system, one TDD radio frame 201 having alength of 10 ms includes two half frames 202. Each half frame 202 iscomposed of five subframes 203. Hence, a TDD radio frame 201 has tensubframes 203, and each subframe 203 is 1 ms long. In the LTE system, asillustrated in Table 1 below, a TDD radio frame may have one of sevenconfigurations according to the number of subframes allocated todownlink and uplink.

In Table 1, ‘D’ indicates a subframe allocated to downlink, ‘U’indicates a subframe allocated to uplink, and ‘S’ indicates a specialsubframe. For example, in configuration 0, subframes 0 and 5 (markedwith ‘D’) are used for downlink transmission, subframes 2, 3, 4, 7, 8and 9 (marked with ‘U’) are used for uplink transmission, and subframes1 and 6 (marked with ‘S’) are special subframes. As indicated byreference numeral 204, a special subframe consists of three fields:DwPTS, Guard Period (GP) and UpPTS. The DwPTS field is used for downlinktransmission, the GP field is not used for transmission, and the UpPTSfield is used for uplink transmission. In a special subframe, as theUpPTS field is small, it is used only for transmitting the PhysicalRandom Access Channel (PRACH) and Sounding Reference Signal (SRS) and isnot used for data or control channel transmission. The GP field is usedto assure a guard time used for switching from downlink transmission touplink transmission.

TABLE 1 Uplink-downlink Downlink-to-Uplink Subframe number configurationSwitch-point periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U UD D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5ms D S U U U D S U U D

Referring to Table 1, some subframes are always used for the samepurpose regardless of configuration. For example, subframes 0, 1, 2, 5,6 and 7 do not change in the ‘ID’, ‘S’ or ‘U’ markings for allconfigurations. Other subframes may change in the ‘ID’, ‘S’ or ‘U’markings according to configuration. In a typical LTE system, once theTDD frame configuration is determined, it does not readily changeaccording to changes in data traffic. It may require at least 80 ms tochange the TDD frame configuration in defiance of interference withneighboring cells. This time of 80 ms is a time that is needed by theuser equipment to receive system update information sent by the basestation and to update the system information without any receptionerror. In reality, it may take 100 ms to several seconds to change theTDD frame configuration. Hence, a scheme to dynamically change the TDDframe configuration may need to be developed. In a TDD frame, subframesthat may dynamically change in downlink/uplink assignment (i.e., dynamicsubframes) are subframes 3, 4, 8 and 9, or subframes 3 and 4.

To switch transmission direction at a specific subframe, the userequipment is to be notified of transmission direction at the subframe ata preset point in time. For downlink transmission, downlink schedulinginformation is effective for the same subframe at which it istransmitted. Hence, downlink scheduling information indicating that agiven subframe is used for downlink transmission may be transmitted atthe given subframe. For uplink transmission, received uplink schedulinginformation applies to uplink transmission at least four subframeslater. Hence, uplink scheduling information indicating that a givensubframe is used for uplink transmission should be transmitted at leastfour subframes before the given subframe. Hence, transmission directionswitching may be accomplished by specifying a control channel carryingscheduling information and a subframe to which the schedulinginformation is to be applied.

However, subframe direction switching through scheduling may cause aproblem. An unscheduled user equipment may repeatedly attempt controlchannel decoding at each downlink subframe even when a control channelassigned to the user equipment is not present. This may cause a channeldecoding error, which may result in simultaneous transmission by thebase station and user equipment at the same time. Consequently,communication performance of the base station and user equipment may bedegraded.

In an exemplary embodiment of the present invention, TDD frameconfiguration information indicating subframe directions is sent as partof system information transmitted on the control channel, so that everyuser equipment may be readily aware of subframe direction switching.This contributes to prevention of link interference and facilitatesrapid system configuration change.

FIG. 3 illustrates a format of generic control channel informationaccording to an exemplary embodiment of the present invention.

In general, control channels have the same basic structure regardless ofcommon control channels and User Equipment (UE)-specific controlchannels. Referring to FIG. 3, the control channel information includesa Downlink Control Information (DCI) part 301 and a Cyclic RedundancyCheck (CRC) part 302. Here, the DCI part 301 is a region for actualcontrol channel information, and the CRC part 302 is a region for anerror detection sequence. The DCI part 301 includes fields 303, 304 and305 for resource allocation information, channel coding information, andother information. In the case of a common control channel, any userequipment may receive system information at a data channel regionindicated by information contained in the fields 303 and 304. Here, theCRC part 302 contains a CRC value scrambled with a Radio NetworkTemporary Identifier (RNTI) known to all user equipments, so that anyuser equipment may receive the control channel information. In the caseof a UE-specific control channel, a specific user equipment may receivea data channel indicated by information contained in the fields 303 and304. Here, the CRC part 302 contains a CRC value scrambled with an RNTIknown only to a particular user equipment, so that only the userequipment may receive the control channel information. As describedabove, generic control channel information is transmitted regardless ofcommon control channels and UE-specific control channels, and isinformation used to receive a data channel carrying actual information.Hence, to deliver updated TDD configuration information in a generalizedway, the base station performs data channel scheduling on the commoncontrol channel and user equipments obtain system information throughdata channel decoding.

FIG. 4 illustrates a format of control channel information according toan exemplary embodiment of the present invention. Here, systeminformation containing TDD frame configuration information is sent onthe common control channel.

Referring to FIG. 4, unlike typical control channel information, actualsystem information is sent on the control channel information region.The common control channel information includes a system informationpart 401 and a CRC part 402. The system information part 401 includes aTDD configuration field 403 and a reserved field 404. The size of thesystem information part 401 is set to that of the DCI part 301. Thereserved field 404 is used so that system information in the systeminformation part 401 always has the same size. When the size of thesystem information part 401 is equal to that of other common controlchannel information, the user equipment may perform blind decoding ofthe control channel through CRC checking without too many decodingattempts. As DCI format 1C is used to transmit the common controlchannel in the LTE system, the size of the system information part 401is set to the size of DCI format 1C. In the CRC part 402, a new RNTI isused to distinguish the proposed control channel information from othercontrol channel information. Table 2 below illustrates RNTIs used in theLTE system.

TABLE 2 Value (hexadecimal) RNTI 0000 N/A 0001-003C RA-RNTI, C-RNTI,Semi-Persistent Scheduling C-RNTI, Temporary C-RNTI, Transmit PowerControl-Physical Uplink Control Channel (TPC-PUCCH)-RNTI andTPC-Physical Uplink Shared Channel (PUSCH)-RNTI 003D-FFF3 C-RNTI,Semi-Persistent Scheduling C-RNTI, Temporary C-RNTI, TPC-PUCCH-RNTI andTPC-PUSCH-RNTI FFF4-FFFC Reserved for future use FFFD M-RNTI FFFE P-RNTIFFFF SI-RNTI

Referring to Table 2, M-RNTI, P-RNTI and SI-RNTI are used for commoncontrol channel transmission using DCI format 1C. In an exemplaryembodiment of the present invention, to transmit TDD configurationsystem information, one of FFF4-FFFC values is assigned to a newTD-RNTI. As shown in Table 3 below, ‘FFFC’ is assigned to TD-RNTI.

TABLE 3 Value (hexadecimal) RNTI 0000 N/A 0001-003C RA-RNTI, C-RNTI,Semi-Persistent Scheduling C-RNTI, Temporary C-RNTI, TPC-PUCCH-RNTI andTPC-PUSCH-RNTI 003D-FFF3 C-RNTI, Semi-Persistent Scheduling C-RNTI,Temporary C-RNTI, TPC-PUCCH-RNTI and TPC-PUSCH-RNTI FFF4-FFFB Reservedfor future use FFFC TD-RNTI FFFD M-RNTI FFFE P-RNTI FFFF SI-RNTI

An exemplary embodiment of the present invention relates to bothtransmission of TDD configuration information and control channelsdelivering system information directly to user equipments without usingdata channels.

TDD configuration information in the TDD configuration field 403notifies user equipments of subframe directions as follows. Table 4below illustrates an exemplary embodiment using two bits, which indicatedirections of subframes 3 and 4 or subframes 8 and 9 (i.e., dynamicsubframes described above). For example, information bits ‘00’ mayindicate that subframes 3 and 4 or subframes 8 and 9 are used for uplinktransmission. The inversed values of the bit patterns defined in Table 4may also be utilized in the same manner. As one control channel isindicated by a maximum of two subframes, a period of 5 ms or a multiplethereof may be used for TDD mode operation.

TABLE 4 Information field Subframe direction 00 U U 01 U D 10 (Reserved)11 D D

Table 5 below indicates subframe direction switching from the uplink tothe downlink. In Table 5, configuration/slot means TDD configurationnumber/slot. For example, 0/1 indicates TDD configuration 0/odd slot,and 0/2 indicates TDD configuration 0/even slot. In Table 5, as thenumber of uplink subframes differs depending upon TDD configurations,the information field may have different numbers of bits. The userequipment identifies the number of bits based on current configurationinformation.

TABLE 5 Configuration Subframe (conf/slot) Information field direction0/1, 0/2, 1/2, 3/1, 6/1, 00 U U 6/2 01 U D 10 (Reserved) 11 D D 1/1,2/2, 4/1  0 U  1 D Else NA NA

Table 6 below indicates subframe direction switching from downlink touplink. In Table 6, as in Table 5, configuration/slot means TDDconfiguration number/slot.

TABLE 6 Configuration Subframe (conf/slot) Information field direction2/1, 3/2, 4/2, 5/1, 5/1 00 U U 01 U D 10 (Reserved) 11 D D 1/1, 2/2, 4/1 0 U  1 D 0/1, 0/2, 1/2, 3/1, 6/1, NA NA 6/2

Table 7 below illustrates a scheme indicating subframe directions usingfour bits. In the case of using 4 bits, a period of 10 ms or a multiplethereof may be used for TDD mode operation.

TABLE 7 Information field Subframe direction 0000 U U U U 0001 U U U D0010 (Reserved) 0011 U U D D 0100 U D U U 0101 U D U D 0110 (Reserved)0111 U D D D 1000-1011 (Reserved) 1100 D D U U 1101 D D U D 1110(Reserved) 1111 D D D D

When a 4-bit information field as in Table 7 is used two times, a totalof 8 bits may be used to indicate directions of eight subframesexcluding subframes 0 and 5. In this case, TDD frame reconfiguration maybe performed in a period of 10 ms.

Table 8 below illustrates a scheme using three bits to directly indicateTDD configuration indexes instead of indicating subframe directions. InTable 8, the information field indicates one TDD configuration andsubframe directions are the same as in Tables 4 through 7.

TABLE 8 Equivalent subframe direction Information field TDDconfiguration (D0, D1, D2, D3) 000 0 U U U U 001 1 U D U D 010 2 D D U D011 3 U U D D 100 4 U D D D 101 5 D D D D 110 6 U U U U 111 (Reserved) —

FIG. 5 depicts control channel transmission for TDD configurationinformation according to an exemplary embodiment of the presentinvention.

Referring to FIG. 5, as directions of subframes 3, 4, 8 and 9 mayfrequently change according to TDD frame configurations, subframes 3, 4,8 and 9 are not suitable for common control channel transmission. Amongthe remaining subframes, subframes 0, 1, 5 and 6 may be used fordownlink control channel transmission. In the case of using a period of5 ms, as indicated by reference numeral 511 of FIG. 5, the userequipment should receive the control channel at subframe 0 indicated byreference numeral 501 and subframe 5 indicated by reference numeral 502.To allow other control channel transmissions using limited commoncontrol channel resources, as indicated by reference numeral 521, TDDconfiguration information may be transmitted at subframe 1 indicated byreference numeral 503 and subframe 6 indicated by reference numeral 504.In an exemplary embodiment of the present invention, as indicated byreference numeral 531, subframes 0, 1, 5 and 6, indicated by referencenumerals 505, 506, 507 and 508, respectively, may be pre-specified ascandidates and the user equipment is directed to attempt to receive thenew control channel at the pre-specified subframes. In another exemplaryembodiment of the present invention, a period and offset are provided sothat the user equipment is allowed to receive the new control channelonly at one of subframes 0, 1, 5 and 6, indicated by reference numerals505, 506, 507 and 508, respectively. When the period is 10 ms and theoffset, indicated by reference numeral 509, is 3, as indicated byreference numeral 541, TDD configuration information may be transmittedat subframe 6 indicated by reference numeral 510 among the fouravailable subframes.

FIG. 6 illustrates timing relationships between reception andapplication of TDD frame configuration information according to anexemplary embodiment of the present invention.

Referring to FIG. 6, as indicated by reference numeral 601, when adirection switch indication is received at subframe 0 or 1, indicated byreference numeral 604, direction switching may be effected at a latertime for both downlink and uplink transmission, as indicated byreference numeral 605. This takes into consideration the time requiredfor the user equipment to receive actual scheduling information afterreception of the corresponding switch indication. That is, a directionswitch indication received at a subframe is effected at a dynamicsubframe at least four subframes later.

In another exemplary embodiment of the present invention, as indicatedby reference numeral 602, a direction switch indication, indicated byreference numeral 606, may be effected at one slot time later for adownlink subframe, indicated by reference numeral 607, and may beeffected at a later time for an uplink subframe, indicated by referencenumeral 608. A downlink subframe may be switched to an uplink subframeimmediately after the direction switch indication as no schedulinginformation is needed, and an uplink subframe may be switched to adownlink subframe at least four subframes thereafter as schedulinginformation is needed. That is, downlink-to-uplink switching is effectedat a dynamic subframe next to the subframe at which the correspondingindication is received, and uplink-to-downlink switching is effected ata dynamic subframe at least four subframes later from the subframe atwhich the corresponding indication is received.

In another exemplary embodiment of the present invention, as indicatedby reference numeral 603, when a direction switch indication, indicatedby reference numeral 609, is transmitted at subframe 0 or 5, it can beapplied to an uplink subframe being the last one in the same half framewhile allowing a delay of at least four subframes, as indicated byreference numeral 611. This corresponds to earliest application of theswitch indication, as indicated by reference numeral 610. That is,downlink-to-uplink switching is effected from a dynamic subframe withinfour subframe's time from the subframe at which the correspondingindication is received, and uplink-to-downlink switching is effectedfrom a dynamic subframe at least four subframes later from the subframeat which the corresponding indication is received.

FIG. 7 illustrates a control channel format for TDD frame configurationinformation according to an exemplary embodiment of the presentinvention. Here, TDD frame configuration information for multiple cellsis aggregated.

Referring to FIG. 7, a scheme in which TDD configuration changes ofdifferent cells are notified by one cell. A user equipment may usemultiple carriers, which are treated as separate cells. When carriersare sufficiently separated in frequency, cells may have different TDDframe configurations and change TDD frame configurations individually.However, to allow user equipments to dynamically acquire configurationinformation, one cell may need to transmit configuration information ofother cells. In FIG. 7, reference numeral 701 indicates a systeminformation part, in which TDD configuration information 703 through 705of multiple cells is linked in order of installed cells. In this case,the size of the system information part 701 should be equal to the totalsize of the common control channel, i.e., the size of DCI format 1C, asindicated by reference numeral 707, in the LTE system. The reservedfield 706 and the CRC part 702 are formed in the same manner as in FIG.4.

In another exemplary embodiment of the present invention, the basestation may send user equipments a MAC header containing TDD frameconfiguration information through a data channel. During data channelscheduling, the base station may transmit a MAC header containing theinformation field described above, and a user equipment may identify anew TDD frame configuration or subframe direction if it successfullyreceives the scheduled data channel.

A MAC header containing TDD frame configuration information may becontained not only in a data channel that is sent by the base station tothe user equipment but also in a data channel that is sent by the userequipment to the base station. Hence, information on the current TDDframe configuration of the user equipment may be fed back to the basestation. This may complement information transmission through the commoncontrol channel, where it is difficult for the base station to determinewhether the sent information is successfully received by all concerneduser equipments. That is, the base station may use this scheme to ensurethat all concerned user equipments use a new TDD frame configuration.

FIG. 8 illustrates a format of a MAC message used to carry TDD frameconfiguration information according to an exemplary embodiment of thepresent invention.

Referring to FIG. 8, the MAC message for a data channel includes a MACheader 801 at the beginning. The MAC header 801 includes multiplesub-headers 809. One sub-header 809 may have a Reserved (R) field 811,an Extension (E) field 813, and a Logical Channel Identifier (LCID)field 815 for sub-header type indication. The LCID field 815 has a sizeof 5 bits for uplink and downlink.

In addition to the MAC header 801, the MAC message includes MAC controlelements 803 (i.e., corresponding in sequence and number to sub-headers809 in the MAC header 801), MAC SDUs 805, and padding 807. A MAC messagemay contain information to be transmitted in a sub-header and associatedMAC control element. Hence, TDD frame reconfiguration information may besent to the user equipment by means of a MAC header. Table 9 belowillustrates LCID values for downlink transmission. Here, LCID value“11010” is assigned to TDD reconfiguration information.

TABLE 9 Index LCID for Downlink Shared Channel (DL-SCH) 00000 CommonControl Channel (CCCH) 00001-01010 Identity of the logical channel01011-11001 Reserved 11010 TDD reconfiguration 11011Activation/deactivation 11100 UE contention resolution identity 11101Timing advance command 11110 Discontinuous Reception (DRX) command 11111Padding

When the base station requests information on the current TDDconfiguration of a user equipment, the user equipment may send currentTDD configuration information to the base station through a MAC message.Table 10 below illustrates LCID values for uplink transmission. Here, anLCID value of “11000” is assigned to TDD configuration reporting.

TABLE 10 Index LCID for UL-SCH 00000 CCCH 00001-01010 Identity of thelogical channel 01011-10111 Reserved 11000 TDD configuration Report11001 Extended Power Headroom Report 11010 Power headroom report 11011C-RNTI 11100 Truncated Buffer Status Report (BSR) 11101 Short BSR 11110Long BSR 11111 Padding

As shown in FIG. 8, a MAC control element having a size of 1 byte, asindicated by reference numeral 817, may be used for transmission of TDDframe configuration information. Such a MAC control element may containan 8-bit information field, as indicated by reference numeral 819,indicating directions of subframes 1, 2, 3, 4, 6, 7, 8 and 9 (excludingsubframes 0 and 5).

FIG. 9 is a flowchart of a transmission procedure for a base stationaccording to an exemplary embodiment of the present invention.

Referring to FIG. 9, the base station transmits TDD frame configurationinformation as system information to the user equipment at step 902. Thebase station then creates a system information element having a sizeequal to the size of DCI format 1C to contain TDD frame reconfigurationinformation at step 903. At step 904, the base station attaches a CRCsequence scrambled with TD-RNTI to the system information element. Thebase station transmits the system information element together with theCRC sequence by allocating the proposed control channel in the commoncontrol channel region of a subframe determined according to a presetperiod and offset or other rule at step 905. The base station performssubframe direction switching in consideration of a timing relationshipbetween the reconfiguration indication and application thereof,schedules downlink transmission and uplink transmission according tosubframe direction switching, delivers the scheduling information to theuser equipment, and performs data channel transmission and reception toand from the user equipment at step 906.

In other words, the base station determines a TDD frame configuration.Here, the base station determines directions of dynamic subframes in theTDD frame according to traffic conditions. The base station generatessystem information based on the TDD frame configuration information.Here, the size of the system information is made equal to the size ofDCI format 1C by adding a suitable number of reserved bits. The basestation attaches a CRC sequence scrambled with TD-RNTI to the systeminformation. If needed, TDD frame configuration information of multiplecarriers can be aggregated into the system information. The base stationtransmits the system information by inserting the system informationinto the common control channel. Thereafter, the base stationcommunicates with user equipments according to the updated TDD frameconfiguration.

FIG. 10 is a flowchart of a reception procedure for a user equipmentaccording to an exemplary embodiment of the present invention.

Referring to FIG. 10, the user equipment receives TDD frameconfiguration information as system information from the correspondingbase station at step 1002. To achieve this, the user equipment attemptsblind decoding, using TD-RNTI, in the common control channel region of asubframe determined according to a preset period and offset or otherrule at step 1003. The user equipment identifies TDD frame configurationinformation from successfully decoded data at step 1004. The userequipment performs control and data channel reception or performs uplinkdata channel transmission in consideration of the indication time andapplication time of the configuration information at step 1005.

In other words, the user equipment receives system information on thecommon control channel. To achieve this, the user equipment performsblind decoding on the common control channel using TD-RNTI defined forTDD configuration system information. Here, the size of the systeminformation is equal to that of DCI format 1C, and TDD frameconfiguration information of multiple carriers can be aggregated intothe system information. The user equipment identifies a TDD frameconfiguration through analysis of the system information. The userequipment determines transmission directions of dynamic subframes in theTDD frame. The user equipment communicates with the base stationaccording to the updated TDD frame configuration. Here, the dynamicsubframes are used according to their transmission directions.

FIG. 11 is a block diagram of a base station according to an exemplaryembodiment of the present invention.

Referring to FIG. 11, the base station includes a TDD Radio Frequency(RF) unit 1101, a dynamic TDD switcher 1102, a transmission handler1103, a reception handler 1104, a controller 1105, a control channelgenerator 1106, a system information attacher 1107, a system informationgenerator 1108, a control information generator 1109, and a controlinformation attacher 1110.

The TDD RF unit 1101 performs radio communication for the base station.The TDD RF unit 1101 performs downlink transmission or uplink reception.The dynamic TDD switcher 1102 controls the TDD RF unit 1101 to switchbetween uplink operations and downlink operations according to presetscheduling times. The transmission handler 1103 processes a signal to betransmitted through downlink transmission. The reception handler 1104processes a signal received through uplink reception. The controller1105 determines a TDD frame configuration. Here, the controller 1105determines transmission directions (i.e., uplink or downlink) of dynamicsubframes. The controller 1105 controls radio communication according tothe TDD frame configuration. Here, the controller 1105 determineswhether to switch transmission directions of dynamic subframes in theTDD frame, and controls transmission direction switching of the dynamicsubframes.

The system information generator 1108 generates system information usingTDD frame configuration information. Here, the size of the systeminformation is made equal to that of DCI format 1C. The systeminformation generator 1108 may generate system information byaggregating TDD frame configuration information of multiple carriers.The system information attacher 1107 attaches a CRC sequence scrambledwith TD-RNTI to the system information. The control informationgenerator 1109 generates DCI. The control information attacher 1110attaches a CRC sequence scrambled with RNTI to the downlink controlinformation. The control channel generator 1106 generates a controlchannel using system information and downlink control information. Thatis, the control channel generator 1106 sends system information anddownlink control information by inserting the same into the commoncontrol channel.

FIG. 12 is a block diagram of a user equipment according to an exemplaryembodiment of the present invention.

Referring to FIG. 12, the user equipment includes a control channelreceiver 1201, a blind decoder 1202, a system information analyzer 1203,a control information analyzer 1210, an RNTI storage 1204, a controller1205, a TDD RF unit 1206, a dynamic TDD switcher 1207, a transmissionhandler 1208, and a reception handler 1209.

The TDD RF unit 1206 performs radio communication for the userequipment. That is, the TDD RF unit 1206 performs downlink reception oruplink transmission. The dynamic TDD switcher 1207 controls the TDD RFunit 1206 to switch between uplink operations and downlink operationsaccording to preset scheduling times. The transmission handler 1208processes a signal to be transmitted through uplink transmission. Thereception handler 1209 processes a signal received through downlinkreception. The controller 1205 determines whether to switch transmissiondirections (i.e., uplink or downlink) of dynamic subframes in the TDDframe based on TDD frame configuration information. The controller 1205controls radio communication according to the TDD frame configuration,and controls transmission direction switching of dynamic subframes inthe TDD frame.

The control channel receiver 1201 performs control channel reception.The blind decoder 1202 receives the common control channel andUE-specific control channel through blind decoding of the controlchannel using RNTIs. The blind decoder 1202 receives system informationon the common control channel using TD-RNTI, and receives downlinkcontrol information on the common control channel using other RNTIs.Here, the system information and downlink control information have thesame size. The RNTI storage 1204 stores various types of RNTIs. Thesystem information analyzer 1203 analyzes system information to identifya TDD frame configuration, and determines transmission directions (i.e.,uplink or downlink) of dynamic subframes. The control informationanalyzer 1210 analyzes downlink control information to identifyscheduling information.

In an exemplary embodiment of the present invention, the method andapparatus for transmitting and receiving TDD frame configurationinformation enable the base station to send TDD frame configurationinformation as system information through the common control channel.Accordingly, the base station may dynamically change the TDD frameconfiguration according to changes in uplink and downlink trafficconditions. In addition, it is possible to prevent interference betweenuplink transmission of the user equipment and downlink transmission ofthe base station.

While the invention has been described with reference to certainexemplary embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the present invention asdefined in the appended claims and their equivalents.

1. A method of transmitting Time Division Duplex (TDD) frameconfiguration information for a base station in a wireless communicationsystem, the method comprising: determining a TDD frame configuration byassigning a transmission direction to a dynamic subframe in a TDD frame;generating system information based on information on the TDD frameconfiguration; and transmitting the system information by inserting thesystem information into a common control channel.
 2. The method of claim1, wherein the generating of the system information comprises making thesize of the system information equal to that of Downlink ControlInformation (DCI) for the common control channel.
 3. The method of claim1, wherein the generating of the system information comprises attachinga Cyclic Redundancy Check (CRC) sequence scrambled with a Radio NetworkTemporary Identifier (RNTI) defined for TDD frame configurationinformation to the system information.
 4. The method of claim 1, whereinthe generating of the system information comprises aggregatingindividual TDD frame configuration information of multiple carriers usedin the wireless communication system into the system information.
 5. Amethod of receiving Time Division Duplex (TDD) frame configurationinformation for a user equipment in a wireless communication system, themethod comprising: receiving system information on a common controlchannel; identifying a TDD frame configuration indicating a transmissiondirection of a dynamic subframe in a TDD frame by analyzing the systeminformation; and utilizing the dynamic subframe according to thetransmission direction thereof.
 6. The method of claim 5, wherein thesystem information has a size equal to that of Downlink ControlInformation (DCI) for the common control channel.
 7. The method of claim5, wherein the receiving of the system information comprises conductingblind decoding of the common control channel with a Radio NetworkTemporary Identifier (RNTI) defined for TDD frame configurationinformation.
 8. The method of claim 5, wherein the system information iscreated by aggregating individual TDD frame configuration information ofmultiple carriers used in the wireless communication system.
 9. Anapparatus for transmitting Time Division Duplex (TDD) frameconfiguration information in a base station of a wireless communicationsystem, the apparatus comprising: a controller for determining a TDDframe configuration by assigning a transmission direction to a dynamicsubframe in a TDD frame; a system information generator for generatingsystem information based on information on the TDD frame configuration;and a control channel generator for inserting the system informationinto a common control channel for transmission.
 10. The apparatus ofclaim 9, wherein the system information generator makes the size of thesystem information equal to that of Downlink Control Information (DCI)for the common control channel.
 11. The apparatus of claim 9, whereinthe system information generator attaches a Cyclic Redundancy Check(CRC) sequence scrambled with a Radio Network Temporary Identifier(RNTI) defined for TDD frame configuration information to the systeminformation.
 12. The apparatus of claim 9, wherein the systeminformation generator aggregates individual TDD frame configurationinformation of multiple carriers used in the wireless communicationsystem into the system information.
 13. An apparatus for receiving TimeDivision Duplex (TDD) frame configuration information in a userequipment of a wireless communication system, the apparatus comprising:a control channel receiver for receiving system information on a commoncontrol channel; a system information analyzer for identifying a TDDframe configuration indicating a transmission direction of a dynamicsubframe in a TDD frame by analyzing the system information; and acontroller for utilizing the dynamic subframe according to thetransmission direction thereof.
 14. The apparatus of claim 13, whereinthe system information has a size equal to that of Downlink ControlInformation (DCI) for the common control channel, and wherein, whenmultiple carriers are used in the wireless communication system, thesystem information is created by aggregating individual TDD frameconfiguration information of the multiple carriers.
 15. The apparatus ofclaim 13, wherein the control channel receiver comprises a blind decoderthat conducts blind decoding of the common control channel with a RadioNetwork Temporary Identifier (RNTI) defined for TDD frame configurationinformation.
 16. A method of transmitting Time Division Duplex (TDD)frame configuration information for a base station in a wirelesscommunication system, the method comprising: inserting TDD frameconfiguration information indicating a transmission direction of adynamic subframe in a TDD frame into a downlink data channel; andtransmitting the downlink data channel to a user equipment, wherein theTDD frame configuration information is contained in a MAC header of thedownlink data channel.
 17. A method of receiving Time Division Duplex(TDD) frame configuration information for a user equipment in a wirelesscommunication system, the method comprising: receiving a downlink datachannel carrying TDD frame configuration information indicating atransmission direction of a dynamic subframe in a TDD frame from acorresponding base station; and utilizing the dynamic subframe accordingto the transmission direction thereof, wherein the TDD frameconfiguration information is contained in a MAC header of the downlinkdata channel.
 18. An apparatus for transmitting Time Division Duplex(TDD) frame configuration information in a base station of a wirelesscommunication system, the apparatus comprising: a wireless communicationunit for sending and receiving a signal to and from a user equipment;and a controller for controlling an operation to transmit a downlinkdata channel carrying TDD frame configuration information indicating atransmission direction of a dynamic subframe in a TDD frame to the userequipment, wherein the TDD frame configuration information is containedin a MAC header of the downlink data channel.
 19. An apparatus forreceiving Time Division Duplex (TDD) frame configuration information ina user equipment of a wireless communication system, the apparatuscomprising: a wireless communication unit for sending and receiving asignal to and from a corresponding base station; and a controller forcontrolling an operation to receive a downlink data channel carrying TDDframe configuration information indicating a transmission direction of adynamic subframe in a TDD frame from the base station and to utilize thedynamic subframe according to the transmission direction thereof,wherein the TDD frame configuration information is contained in a MACheader of the downlink data channel.